Biomedical articles, particularly those which are in contact with blood, require certain properties to ensure acceptance by the body and body tissue for incorporation into the body on a long-term basis.
Prosthetic arterial replacements in humans to correct impaired arterial flow are well accepted. Grafts of polyester, tetrafluoroethylene and other synthetic materials are commonly used where the diameter of the arterial replacement is generally greater or equal to six millimeters; however, synthetic vascular prostheses with diameters less than six millimeters have not been conventionally employed, generally because of the increased probability of the development of obstructions due to thrombosis and/or vessel wall thickening.
The search for an ideal prosthetic arterial graft began some 25 years ago, with research and development focusing on smooth-walled, non-thrombogenic "inert" implants. Ideas centered around Teflon and Dacron low-porosity weaves which did not require preclotting, as there was no blood leakage at surgery. Over the past 10 years, more "reactive" or initially thrombogenic grafts have increasingly been used in surgical applications. Knits, external and finally internal velours appeared, all of which were porous, increasingly textured surfaces requiring preclotting. These seemed to be better incorporated into the body on a long-term basis, both in terms of external tissue fixation by fibroblast ingrowth through the pores and possibly also through the luminal anchoring of a non-thrombogenic, biologically passivated surface.
The real challenge for vascular substitutes today is the smaller diameter (&lt;4 mm) and/or low blood flow situation as is encountered in the femoral-popliteal region, or more importantly, in the coronary arteries. While patency rates run as high as 99% at 5 years in aortic grafts, femoral-popliteal grafts exhibit 50-70% patency at 5 years at best. Coronary artery replacement by prosthetic materials has barely been attempted.
Porous polytetrafluoroethylene tubing for use in vascular grafts is described in U.S. Pat. Nos. 3,962,153 and 3,953,566. U.S. Pat. No. 4,304,010 describes the application of a porous elastomeric coating over the outside surface of stretched porous polytetrafluoroethylene tubing for use in vascular grafts. U.S. Pat. No. 4,321,211 describes incorporating an anticoagulant substance in a stretched porous polytetrafluoroethylene material and incorporating an outer porous elastomeric coating around the PTFE material containing a substance which counteracts the anticoagulant substance. U.S. Pat. No. 4,208,745 describes a stretched PTFE polymer in which the fibrous structure on the inside surface is made up of finer fibers than the fibrous structure on the outside surface face. U.S. Pat. No. 4,193,138 describes the preparation and use of stretched porous PTFE materials in which the pores are filled with a water-insolubilized, water-soluble polymer, such as polyvinyl alcohol. U.S. Pat. No. 4,312,920 describes surface modification of polyurethane with an alloy of silicone rubber, the material being useful in the fabrication of biomedical articles. U.S. Pat. No. 4,254,180 describes the preparation of a heparin-receptive surface on a mixture of a particulate resin and a graphite. U.S. Pat. No. 4,265,927 discloses heparinizing a charged surface of a biomedical article with a fine-grained, colloidal aqueous solution of a complex compount of heparin and a cationic surfactant. U.S. Pat. No. 4,116,898 describes coating a polymeric substrate with a particular compound incorporating a heparin-like substance. U.S. Pat. No. 4,179,751 discloses the use of poly(alpha-olefin-sulfone) membrane prepared from C.sub.8 -C.sub.18 alpha-olefins and sulfur dioxide for use in biomedical articles. U.S. Pat. No. 4,042,978 describes preparation of a plastic for prosthetics made up of repeating units having the structure --CH.sub.2 --CH.sub.2 --O--. U.S. Pat. No. 3,853,062 describes use of a knitted linear polyester fabric which has been treated with a compacting solution for use as a vascular graft. U.S. Pat. No. 3,839,743 describes preparation of a thrombo-resistant article made by coating a surface in contact with blood with an organic polymeric material having fluoroalkyl side chains of the formula C.sub.n F.sub.2n+1 C.sub.m C.sub.2m --. U.S. Pat. No. 4,167,045 describes the use of a woven Dacron material which has its surface modified to make it thrombo-resistant. U.S. Pat. No. 4,178,329 describes a graft copolymer of a particular type for use in fabrication of biomedical materials for biomedical uses. U.S. Pat. No. 4,047,252 describes a double-velour, synthetic vascular graft made of Dacron. U.S. Pat. No. 3,940,802 describes a blood bag fabricated from plasticized polyvinyl chloride and a thermoplastic polyester-based polyurethane. U.S. Pat. No. 4,319,363 describes a tube of collagenous tissue subjected to glutaraldehyde tanning to give cross-linked collagen fibrils for use as vascular graft material.
A review of the safety and performance of currently available vascular prostheses can be found in Vol. 4, No. 4, American Society for Artificial Internal Organs, J. D. Mortensen, "Safety and Performance of Currently Available Vascular Prostheses." This article also references a comprehensive literature search performed for the Federal Food and Drug Administration by the Utah Biomedical Testing Laboratory on vascular grafts and their safety.